1. Field of the Invention
The present invention relates to a magnetic sensing element including a free magnetic layer, a nonmagnetic conductive layer, and a pinned magnetic layer, and in particular, to a magnetic sensing element pinning the magnetization of the pinned magnetic layer by means of a uniaxial anisotropy of the pinned magnetic layer itself.
2. Description of the Related Art
Recently, among magnetic heads mounted in magnetic recording and playback devices, a spin-valve magnetic sensing element using the giant magnetoresistive (GMR) effect is widely used.
The spin valve magnetic sensing element includes a ferromagnetic film called a pinned magnetic layer, a ferromagnetic soft magnetic film called a free magnetic layer, and a nonmagnetic film called a nonmagnetic conductive layer disposed therebetween.
The magnetization of the free magnetic layer is aligned in one direction by a longitudinal bias magnetic field from, for example, hard bias layers composed of a hard magnetic material. The magnetization of the free magnetic layer is sensitively changed in response to an external magnetic field generated from a recording medium. On the other hand, the magnetization of the pinned magnetic layer is pinned in a direction that crosses with the magnetization direction of the free magnetic layer.
The electrical resistance is changed according to the relationship between the above change in magnetization direction of the free magnetic layer and the pinned magnetization direction of the pinned magnetic layer. A leakage magnetic field from the recording medium is detected by changes in voltage or current based on the change in the electrical resistance.
In the known art, the pinned magnetic layer is formed on an antiferromagnetic layer composed of an antiferromagnetic material such as PtMn. An exchange coupling magnetic field is created between the pinned magnetic layer and the antiferromagnetic layer, thereby pinning the magnetization of the pinned magnetic layer.
However, the antiferromagnetic layer must have a thickness of about 200 Å in order that the exchange coupling magnetic field generated at the interface between the antiferromagnetic layer and the pinned magnetic layer has a sufficient intensity.
An antiferromagnetic layer having a large thickness disposed in the laminated component of a magnetic sensing element mainly causes a shunt loss of a sense current. In order to achieve a high recording density on the recording medium, the output of the magnetic sensing element must be improved. However, the shunt loss of the sense current prevents improvement of the output of the magnetic sensing element.
Furthermore, a top shield layer and a bottom shield layer, which are composed of a soft magnetic material, are disposed on the magnetic sensing element and under the magnetic sensing element, respectively, in order to effectively read recording signals to be detected. In order to achieve a high linear recording density on the recording medium, the distance between the top shield layer and the bottom shield layer must be small. The antiferromagnetic layer having a large thickness also prevents the distance between the top shield layer and the bottom shield layer from being small.
Consequently, a magnetic sensing element that does not include the antiferromagnetic layer has been proposed. The magnetic sensing element pins the magnetization of the pinned magnetic layer by means of a uniaxial anisotropy of the pinned magnetic layer itself.
For example, patent documents in the known art include U.S. Pat. No. 6,456,469B1, and Japanese Unexamined Patent Application Publication Nos. 8-7235 and 2000-113418.
According to U.S. Pat. No. 6,456,469B1,the magnetization of a first anti-parallel (AP) pinned layer 416 forming a pinned magnetic layer is pinned using an antiferromagnetic (AEM) layer 410. Therefore, this magnetic sensing element is different from the above magnetic sensing element in which the magnetization of the pinned magnetic layer is pinned by means of uniaxial anisotropy of the pinned magnetic layer itself.
According to the above patent document, a buffer layer 412 is disposed between the AFM layer 410 and the first AP-pinned layer 416. Referring to line 38 to line 40 in the seventh column, the use of the buffer layer 412 improves the GMR coefficient. Although there is not a specific description, the buffer layer 412 may be a magnetic layer because an exchange coupling magnetic field must be successfully generated between the AFM layer 410 and the first AP-pinned layer 416.
In the magnetic sensing element disclosed in the above patent document, the magnetization of the first AP-pinned layer 416 is pinned by means of the exchange coupling magnetic field using the AFM layer 410. In such a case, the AFM layer 410 has a very large thickness (see line 18 and the following lines in the seventh column of the patent document). As a result, as described above, the shunt loss of the sense current prevents improvement of the output of the magnetic sensing element.
In contrast, according to magnetic sensing elements disclosed in Japanese Unexamined Patent Application Publication Nos. 8-7235 and 2000-113418, the magnetization of a pinned magnetic layer is pinned by means of a-uniaxial anisotropy of the pinned magnetic layer itself without using an antiferromagnetic layer.
According to the above patent documents, the pinned magnetic layer has a synthetic-ferri-pinned structure (a structure in which a nonmagnetic interlayer is disposed between two magnetic layers). The magnetization of the pinned magnetic layer is pinned by adjusting the magnetic moment (Japanese Unexamined Patent Application Publication No. 8-7235) or by controlling, for example, the material of the pinned magnetic layer (Japanese Unexamined Patent Application Publication No. 2000-113418).
In order to adequately pin the magnetization of a pinned magnetic layer without using an antiferromagnetic layer, the magnetostriction constant or the coercive force of the pinned magnetic layer must be increased. However, the optimization of the pinned magnetic layer as disclosed in the above patent documents cannot sufficiently increase the magnetostriction constant or the coercive force.
In particular, regarding the magnetostriction constant of the pinned magnetic layer, even when the magnetization of the pinned magnetic layer is pinned in the direction parallel to the height direction by optimizing the magnetostriction constant, the following problem occurs. When an excessive stress (hereinafter may be referred to as mechanical stress) is applied on the magnetic sensing element, the magnetization of the pinned magnetic layer directed in the direction parallel to the height direction is reversed. In particular, when the coercive force of the pinned magnetic layer is small, the magnetization of the pinned magnetic layer may be reversed even in the direction parallel to the track width direction. Such an excessive stress is applied during the manufacturing process of the magnetic sensing element. Such an excessive stress is also applied, for example, when the magnetic sensing element is hit with a projection on a medium during floating on the medium.
In such a case, after the above stress is removed, the change in the magnetization direction of the pinned magnetic layer, which has unintentionally directed in the track width direction, cannot be expected. In other words, it cannot be expected whether the magnetization direction of the pinned magnetic layer is returned in the direction away from a medium or in the direction toward the medium, both of the directions being parallel to the height direction. As a result, in shipping or during practical use of the magnetic sensing element, the magnetization direction of the pinned magnetic layer of the magnetic sensing element is readily changed to reverse in the direction opposite to the regulated direction.